Magnetic limit switch



JulyIZ, 1949. c. F. COAKE MAGNETIC LIMIT SWITCH 2 Sheets-Sheet 1 Filed Feb. 24, 1945 I INVENTOR 6/4/2455 A 60am:-

. 4 If, I

TORNEY C. F. COAKE MAGNETiC LIMIT. SWITCH July 12, 1949.

2 Sheets-Sheet 2 Filed Feb. 24, 1945 I I NVENTOR CHAPAfJ' fife/1m:

ATTORNEY Patented July 12, 1949 EI MAGNETIC LIlWI-Ti SWI'IEH 1' CharleST.F.I.Coake,. Indianapolialilnd .assignoreto "fSennTCorporation, New Augusta,"ln'd., a corporation-of Indiana eApplioation February 24, 1945;:Setial No; 579,629

15" Claims. 1

.IIYhis I invention relates .to .-a tmicrorgauge limit ,switchland it has for; its object toprovide a novel and. improved device of: thisstype.

Another object: .of the invention is to provide an extremely sensitive. positive-acting magnetic isnap. switchifor detecting l minute-variations f rom astandard limit .ot comparison.

.uknotlrier object .is to rprovide -.a ,simple and .eflioient Inicrowgauge limitsswitch of the above type .having. novel a-and improved, details; of construction and features vof operation.

I Warioustother objects and .advantageswill :be apparent as -thel nature of I the inventionis more fully disclosed.

1 The limit switchlofr my invention is particularly -adapted.torithe-itestingof production/items which ,mustrconformiWithinl-a close limit oftolerance withraagiven-cstandard Lof -.-.Ineasurement. aThe .s-w-itoh: "disclosed. herein-to illustrate :the invention ineiudesra-styluswhich isadapted.-tobe actuated byzth itemibeingitestedlarrd which; isiconnected .touclose: arsnapf contactin iresponse-Jto. any .varia- .tions vbEYOIld the predetermined :iirnit of tolerance.

The microegauge limits-switch itself -preferably icompriseszamagneticcircuitcontaining an-armature which is delicately balanced on self-adjust- .ing hearings and cooperates with a -magnetic frame which provides two normally lbalancedi re- .12 n lthoughithepnovell features which are characteristic of thisinventioniaresset forth more in .l-detailz inxthelclaimsaappendedz hereto, thev nature and scope; f+the-z invention may be betterunder- 'astood cbyl referring to .the following .description,

.taken in connection with the accompanying drawings forming a part thereof,=in Whichsa-spe- .ciiicrem-bodirnenthaswbeeniset forth for vpurposes .of illustration.

lzInithe :drawings Fig. il-issa broken.-perspectiveviewof :amicro- .igaiuge limit switcha.emhodyingithe. invention;

F igl- 2v isea -longitud-inala sectional View taken .onltheiine 2:2- .0f:Fig;.- .1;

"-EigJB is.-a;f11ont end elevation of. the device;

Fige-eis can enlarged transverse. sectional view taken onthei *line-:4-4;of- Figs 2;

:5wis1 a transverse sectional view .taken on Ethel line -US-T-S -.of1 Fig.1 2 and Fig. 6 is a section taken-ion the line- 6--6 of Fig- 2. v

:.In sthe following description certain specific terms are used for convenienceinreferring-to therizariousldetails of the invention. These terms, howeverare to be interpretedflas broadly as the .25 .state' of-lthe artwill permit.

ltur-n -paths .for. the magnetic flux; passing? through ;the :.armature. The gaugessty-lusi isfsupportedeon springs in an upright; position wand l is :provided with an adjustable :iilangerwhich is adapted to engage L beneath the 4 armature-T end -.-to move the armature upwardly in response to movement-of I ment with thencr0ss=bar. nAtco-ntactis actuated bythe armature titer-closean indicator. circuit which will; infer-m L-the operatorcof i the: 'fdQfBCt: in theiarticle under test. lProductiongparts maythus he rapidly. and-vaccunatelyfitested loy an unskilled operator, the warning signal indicatingithatl the part is to be discarded.

- The-2.contacts.-.remai-nnopen until. i the magnetic .balancevis upset, whereupon they vclose with :8, snapzlaction. .i-Hence-r';ehattering :01 other uncertainty inooperationxis eliminated.

:The .-miero-gauge limittswitchsshown inithe drawings mom-prises can ,electromagnet -.-coi1- ill mounted cone-a hollow tsupport l l .and secured to v.a Ueshaped .frame- .of 1 magnetic material which hasnparallel i pper and. lower horizontal. branches 42mm -|.3 Joined byaantend portion M! and :is supported Joynscrevvs. l5 and-l6 on a suitable .bracket l'l.

:.-/An..larmature- I 8 is mountedv centrally in the -coil- Land has-its iorwardend-hifuroated to proivideespaced. upper -and lowernprongs l9 and 12B extending-outwardly through a circular opening 52 l=-in the-rend; portion l4;of. the frame and having ears-1.22 and i23aat its-:reanend. arranged inproximity to the branches I2 and I3, respectively; of .the frame toniorm=a,pa1t oftthevmagnetic circuit. :Thesupport. for; therarmature l8: includes a-spair rofflanged bracketsiziaanddfi which are secured .torthesbranchesr I 2 wand 13: of the frame hyJmeanS :of: screws 21 andi28;.respectively. The'end flanges of athese brackets; face each: other, and fiat. con.- .-voluted iresiiientsprings 2 9 and 38 are secured .to -the. .op posed .'--flanges by. means of escrews -3 l randwl32, w'respectively. .The springs 29 wand '31] lareiseshaped to provide increased compliance. an d the-n-centralaportions thereof contain aligned .ta-peredliconioal indentations--33 and 34, lrespeo- ;ti-vely. In thesepindentations ware journaled the repainted.- ends ofyaspintleor arbor-35-=which is se- -cured-cto andtthusasupportsi the-armature l 8. The :springs 29 and 30sareiflexed: slightly toward each .othertso': that the; far-mature; pintle-35 will I main- "tain its'r:del-ioate1y.- balanced mounting "and will .beself .--adji1sting to i compensate 1. forwear.

=r-Aaflatestationarytcross bar 13B is ssecuredtorthe frame of the electromagnet by screws 31 and extends between the upper and lower prongs I9 and 28 of armature |8 in such position that said prongs will be equidistant from said cross bar, as shown in Figs. 2 and when the armature I8 is in its mid-position. The lower face of cross bar 36 has a facing 38 of non-magnetic material such as copper to prevent the lower prong of the armature from sticking thereto due to residual magnetism.

A vertical gauge stylus 39 is flexibly supported by leaf springs 49 and 4| which are secured to the respective upper and lower branches I2 and I8 of the magnetic frame by screws l5, l6 and 42, the spring 4| being spaced from the magnetic frame by suitable washers 43 as shown in Figs. 1, 2 and 4. The stylus 39 carries a flange or washer 4-4 which is adjustably clamped thereon by threaded nuts 45, and this flange 44 engages a ball 48 which is secured to the underside of the lower prong 20 of the armature l8, as shown in Figs. 2 and 5.

The contact members 48 and 49 for closing the indicator circuit (not shown) are carried by contact springs 50 and 5| respectively, which are provided with T ends secured between bracket ll and the upper branch |2 of the frame by the screws l5 and I6. Contact springs 50 and 5| are provided with terminals 52 and 53 respectively and are insulated from the frame by suitable insulating washers 54 and from the screws [ii and It by insulating bushings 55. The terminals 52 and 53 are connected to any suitable visual or audible signaling system. Stop members 59 and 5'! may be associated with the contact springs 59 and 5| respectively, and may be adjusted for properly positioning same.

The lower contact spring 5| has a portion of its forward surface stamped out and bent downwardly to provide a depending lip 58 which lightly engages the top face of the upper prong l9 of the bifurcated armature l8, as best shown in Fig. 2. Accordingly, when the armature I8 is turned upon its pivot in a counter-clockwise direction as viewed in Fig. 2, until the lower prong 29 of the armature strikes the non-magnetic liner 38 of the stationary cross bar 36, the upper prong [9 of the armature will raise the depending lip 58 of contact spring 5|, thus causing contact member 49 to engage the contact member 48 and close the energizing circuit of the alarm system. The magnetic attraction will hold the armature in this circuit closing position until forcibly returned or until the coil I0 is deenergized.

In operating the micro-gauge limit switch described above, let it be assumed that the stylus 39 is adjusted to gauge the thickness of a series of articles which are supposed to conform to a certain standard within a predetermined limit of tolerance. The micro-gauge in this instance is intended to pass all the articles which do not exceed the limit of tolerance, and to give a warning signal or alarm in the case of any article which does exceed the limit even to an infinitesimal degree so that such faulty article may be discarded. In carrying out the test, the articles are successively placed beneath the lower end of the stylus 39 in any suitable manner, not shown herein, and the gauge is adjusted by the nuts or by setting the bracket so that at the limit of tolerance the armature I8 is in balanced position with the prongs l9 and 20 spaced equally from the stationary cross bar 36 as shown in Figs. 2 and 5. In this position the magnetic flux set up by coil |0 flows from the armature l8 through both prongs l9 and 2!] equally to the magnetic cross bar 36 and then through the upper and lower branches l2 and I3 of the frame which constitute magnetic return paths to ears 22 and of the armature. At such time, therefore, the magnetic flux through the two paths will be in state of balance, and this balance will not be disturbed when an article not exceeding the predetermined limit of tolerance is placed beneath the lower end of the stylus 39.

However, when an oversize article is placed beneath the lower end of stylus 39, even though the excess thickness of the article may be infinitesimal, it will cause the stylus to rise slightly beyond its mid-position and the stylus, through its flange 44 and contact ball 46, will cause a corresponding very slight tipping of the armature If; in a counter-clockwise direction as viewed in Fig. 2. This movement will upset the magnetic balance of the gauge and the magnetic pull of the cross bar 38 becomes greater on the lower prong and will cause the armature l8 to continue its movement with an instantaneous snapaction. bringing the lower prong 29 of the armature into contact with the non-magnetic liner 38 of stationary cross bar 36, and closing the contacts 48 and 49 with a snap action.

When the armature is displaced below its midposition the magnetic effect will tend to pull the same downwardly but this effect is resisted by the stylus. On its upward movement it is able to leave the stylus as the ball 45 only rests lightly on the disc 44. Hence a controlled upward movement is obtained which becomes a snap-action as soon as the armature passes its mid-position.

The springs 40 and 4| are of sufficient strength to hold the stylus 39 firmly against the test article.

The stop members 56 and 51 may be adjusted to provide the desired spacing of the contacts 48 and 49.

It will be noted that the S shape of the springs 29 and 39 provides a much greater pliability than a straight spring of the same length. The elements may be made of suitable spring material such as Phosphor bronze which provides relatively high flexibility. Hence the pintle 35 is lightly but firmly held in a bearing having negligible friction.

The above described mechanism provides an extremely accurate limit switch which operates in response to minute variations in position of the stylus.

It is to be understood that the balanced magnetic paths may take other forms. For example the end of the armature could be mounted between upper and lower pole pieces instead of having bifurcation cooperation, with a single cross 60 bar as shown, the essential feature being to pro- Vide a structure in which the magnetic pull is equalized when the armature is in its mid-position but causes the armature to snap to a limiting position when the balance is upset.

Although a specific embodiment has been shown and described herein for purposes of illustration, it will be evident to those skilled in the art that the invention is capable of various modifications and adaptations within the scope of the appended claims.

The invention claimed is:

1. An electromagnet comprising a pivoted armature having a bifurcated end forming two prongs, a stationary magnetic member positioned 76 between said prongs and equally spaced theresaid frame, a stylus carried by said spring members and means on said stylus engaging said armature to displace the same from its mid position, the magnetic flux flowing from said armature to said end piece and returnin through the upper and lower branches of said frame, whereby micro movement of said armature due to said stylus -will upset the magnetic balance of said flux paths and cause said armature to snap to a limiting position.

11. In a relay having contacts, a magnet comprising a U-shaped magnetic frame having upper and lower parallel branches and a connecting end piece, an armature mounted between said parallel branches and having an end projecting out wardly through said end piece, magnetic means secured to said frame and cooperating with projecting end of said armature to produce bal-- anced magnetic forces when said armature is in its mid-position, sprin members mounted on said upper and lower branches of said frame, a stylus carried by said spring members and means on said stylus engaging said armature to displace the same from its mid-position, the magnetic flux produced by said magnetic means fiowing from said armature to said end piece and returning through the upper and lower branches of said frame, whereby micro movement of said armature due to said stylus will upset the magnetic balance of said flux paths and cause said armature to snap to a limiting position, and means actuated by said snap movement of said armature to close said contacts with a snap action.

12. In a relay having contacts, a magnet comprising a U-shaped magnetic frame having upper and lower parallel branches and a connecting end piece, an armature mounted between said parallel branches and having an end projecting outwardly through said end piece, magnetic means secured to said frame and cooperating with the projecting end of said armature to produce balanced magnetic forces when said armature is in its mid-position, spring members mounted on said upper and lower branches of said frame, a stylus carried by said sprin members and means on said stylus engaging said armature to displace the same from its mid-position, the magnetic flux produced by said magnetic means flowing from said armature to said end piece and returning through the upper and lower branches of said frame, whereby micro movement of said armature due to said stylus will upset the magnetic balance of said flux paths and cause said armature to snap to a limiting position, a pair of spring members carried by said upper branch of said frame and carrying said contacts, and a link engaging said armature to close said contacts in response to said snap movement of said armature.

13. A magnet comprising a magnetic frame having upper and lower parallel branches, flat S-shaped resilient armature-supporting springs extending between said upper and lower branches of said frame on opposite sides thereof and containing aligned conical indentations therein, an armature-supporting pintle having corresponding conical ends journaled in said indentations, said spring being flexed toward each other to maintain their engagement with said pintle, an armature on said pintle extending between said branches, magnetic means on said frame forming poles exterting a balanced magnetic force on said armature when the armature is in its mid-position, and means for displacing said armature from its mid-position to cause said armature to snap to a limiting position in response to the unbalanced magnetic forces.

14. A micro-gauge limit switch having contacts, comprising a Ll-shaped magnetic frame having upper and lower parallel branches and a connecting end piece, a coil secured to said end :5. between the upper and lower branches of said frame, a pivoted armature extending through said coil and having a bifurcated end forming upper and lower prongs projecting outwardly through said end piece, a cross bar secured to said end piece and extending between said prongs and lying equidistant from said prongs when said armature is in its mid-position, a stylus mounted for movement on said frame, a

adiustably mounted on said stylus to engage the under side of said lower armature prong, and a link resting on the upper prong of said armature to close said contacts when said armae n its upper limiting position, the magetic i x set up by said coil flowing from said armature through both armature prongs to said cross and returning through the upper and lower branches of said frame, whereby displaceof said armature from its mid-position by :2 stylus will upset the magnetic balance of said flux paths and cause said armature to snap to limiting position.

15. A micro-gauge limit switch having contacts, comprising a U-shaped magnetic frame having upper and lower parallel branches and a connecting end piece, a coil secured to said end piece between the upper and lower branches of said frame, a pivoted armature extending through said coil and having a bifurcated end forming upper and lower prongs projecting outwardly through said end piece, a cross bar secured to said end piece and extending between said prongs and lying equidistant from said prongs when said armature is in its mid-position, stylus mounted for movement on said frame, a flange adiustably mounted on said stylus to engage the under side of said lower armature prong, and a link resting on the upper prong of said armature to close said contacts when said armature is in its upper limiting position, the magnetic flux set up by said coil flowing from said armature through both armature prongs to said cross bar and returning through the upper and lower branches of said frame, whereby displacement of said armature from its mid-position by said stylus will upset the magnetic balance of said. flux paths and cause said armature to snap to its limiting position, and a spacing member of non-magnetic material interposed between said cross bar and said armature to prevent said armature from sticking thereto due to residual magnetism.

CHARLES F. COAKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 808,834 Goodrum Jan. 2, 1906 890,22) Crane June 9, 1908 1,085,721 Berdon Feb. 3, 1914 1 693,313 Murphy Nov. 2'7, 1928 2,119,450 Trautner May 31, 1938 2,145,950 Persons Feb. '7, 1939 2,260,813 Wilson Oct. 28, 1941 

